and clearly that was "harry potter." and in a very, very different, it's also "the casual vancy." >> reporter: you've gone -- it seems to me -- from the ultimate fantasy to the ultimate reality. >> i have gone from dragons and unicorns and all the fun that's involved in writing that to a book that's intensely personal, that expresses a lot of my reality. >> reporter: rowling insists the book isn't a memoir but she did draw on the darker times of her life to craft her characters. >> we have an adult character in the book who has obsessive-compulsive disorder. and these are -- these are things i know from the inside, yeah. >> reporter: the ocd part of it as well? >> when i was in my teens, i had issues with ocd. >> reporter: how did it manifest? >> compulsions. >> like? >> checking things. you know, it's very common. checking, double checking, triple checking. >> reporter: some might wonder why rowling, an almost billionaire, would bother writing another book -- putting her reputation on the line. so how will you decide wh